The board-writing emote in Jujutsu Shenanigans is called Message. A Reddit post in the game’s community specifically answers it that way.

How to use it

Once you have the emote, equip or trigger Message in-game and it should let your character write on a board or surface, depending on the mode/version you’re on. One community guide also refers to a related “text on the top” setup for build-mode-style text, which suggests the feature is tied to placing or displaying text rather than a separate weapon or item.

Quick note

Some search results about “how to get the board” appear to be low-quality or misleading, so the clearest verified name here is just Message.